JP4943634B2 - Method for purifying alkoxystyrene polymer - Google Patents

Description

Background of the Invention Copolymers and terpolymers are mixtures of compounds of various compositions and molecular weights when isolated from a reaction solution. Typically they contain small amounts of starting materials and by-products that are undesirable in the final polymer. The polymer mixture is precipitated from the solvent or solvent mixture by adding the mixture to a second solvent such as, for example, water, hexane, heptane, octane, petroleum ether or mixtures thereof. The polymer is then dried under a nitrogen atmosphere. The object of the present invention relates to a method for purifying polymers.

  Davidson, in US Pat. No. 5,945,251, forms a purified polymer by adding amine, hydrophilic solvent, hydrophobic solvent and water to the polymer; separating the aqueous phase; and then removing the hydrophilic and hydrophobic solvent Discloses a method for purifying polyhydroxystyrene polymers.

In US Pat. Nos. 5,789,522 and 5,939,511, Zepmini et al. Extract impurities from the resin by dissolving a phenol resin in a photoresist solvent and extracting water-soluble impurities therefrom.
SUMMARY OF THE DISCLOSURE The present invention provides a novel method for improving the glass transition temperature and reducing polydispersity values of polymer intermediates polymerized by precipitation from methanol. The polymer that can be treated by the method of the present invention is a polymer of 4-acyloxystyrene. The 4-acyloxystyrene derived polymer is then transesterified to 4-hydroxyphenyl containing polymers useful for paints, resins, thickeners and photoresist compositions. The method of the present invention is an improvement over the prior art and is extremely effective. Specifically, the present invention provides a method for removing unreacted monomers, low molecular weight polymers, etc. from the crude polymer mixture prior to the transesterification step. A number of analytical methods are available to quantify improvements in polymer purity. Average molecular weight, nuclear magnetic resonance, chromatography and glass transition temperature are all useful in some instances with constant molecules and characteristic side chains.

As previously described in the prior art, the polymerized crude polymer is separated from the alcohol by filtration, centrifugation, decantation, and the like. According to the method of the present invention, the polymer is subjected to separation , whereby it is suspended in methanol and the solid is separated from methanol. This procedure is repeated for as long as necessary to remove by-products and low molecular weight materials that are more soluble in methanol than the desired polymer. In this way, undesired monomer impurities and oligomers are dissolved in a solvent (such as methanol) depending on the temperature and are thus removed during each separation step.
DETAILED DESCRIPTION OF THE INVENTION The present invention provides monomers I

Wherein R is —C (O) R ⁵ or —R ⁵ ; a homopolymer or typically the following monomer: an acrylate monomer having formula II

1 or more and / or styrene, 4-methylstyrene, styrene alkoxide (alkyl moiety is a linear or branched C ₁ -C _5), tert- butylstyrene, cyclohexyl acrylate, tert- butyl acrylate, improvement in its composition as a copolymer with one or more ethylenically unsaturated copolymerizable monomers (EUCM) selected from the group consisting of tert-butyl methacrylate, maleic anhydride, dialkyl maleate, dialkyl fumarate and vinyl chloride Provide a way for:
In the above formula,
i) R ¹ and R ² are the same or different,
hydrogen;
Fluorine, chlorine or bromine;
Alkyl or fluoroalkyl group having the formula C _n H _x F _y (wherein, n is an integer from 1 to 4, x and y are integers of 0 to 2n + 1, the sum of x and y is 2n + 1) And independently selected from the group consisting of phenyl or tolyl;
ii) R ³ is selected from the group consisting of hydrogen; and methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl and tert-butyl;
iii) R ⁴ is methyl, ethyl, n-propyl, iso-propyl, n-butyl, i-butyl, tert-butyl, t-amyl, benzyl, cyclohexyl, 9-anthracenyl, 2-hydroxyethyl, cinnamyl, adamantyl , Methyl or ethyl or hydroxyl adamantyl, isobornyl, 2-ethoxyethyl, n-heptyl, n-hexyl, 2-hydroxypropyl, 2-ethylbutyl, 2-methoxypropyl, 2- (2-methoxyethoxyl), oxotetrahydrofuran, hydroxy Trimethylpropyl, oxo-oxatricyclononyl, 2-naphthyl, 2-phenylethyl, phenyl, etc .; and
iv) R ⁵ is C ₁ -C ₄ alkyl;
The polymer is typically a monomer of formula I:

  Or a monomer of formula I and / or monomer II and / or one or more of said copolymerizable monomers (EUCM) in a corresponding composition at a suitable temperature in an alcohol solvent and in the presence of a free radical initiator By subjecting it to suitable polymerization conditions for a time sufficient to produce. After purification by the method of the present invention, the purified polymer has formula III

Is transesterified to a polymer containing the following monomers:
(1) In the presence of a catalytic amount of a base catalyst in the alcohol solvent, the transesterified by-product ester produced is continuously removed from the reaction mixture to yield a homopolymer of I or I and / or II, and / or The polymer is subjected to transesterification conditions at a suitable temperature to form a copolymer of the copolymerizable monomer (EUCM), or (2) the polymer is subjected to acidic hydrolysis with a strong acid. The polymer is then optionally removed through an ion exchange bed to remove the base or acid catalyst.

  It is also within the scope of the present invention to prepare homopolymers of formula I from monomers of formula III. In another embodiment, polyhydroxystyrene (PHS) can be prepared from acetoxystyrene monomer (ASM).

  Thus, the scope of the present invention is (a) a homopolymer of formula I derived from a monomer of formula III; (b) a copolymer derived from monomers of formula II and formula III; (c) a monomer of formula III and Copolymers derived from EUCM; and (d) monomers of formula II, formula III and terpolymers derived from EUCM. It is also within the scope of the present invention to form crude polymer products that are processed by the novel process of the present invention using other monomers such as norbornene monomers, fluorine monomers.

  In connection with Formula II (acrylate monomer) described herein, some preferred acrylate monomers are (1) MAA-methyladamantyl, (2) MAMA-methyladamantyl methacrylate, (3) EAA-ethyladamantyl. Acrylate, (4) EAMA-ethyladamantyl methacrylate, (5) ETCDA-ethyltricyclodecanyl acrylate, (6) ETCDMA-ethyltricyclodecanyl methacrylate, (7) PAMA-propyladamantyl methacrylate, (8) MBAMA-methoxy Butyl adamantyl methacrylate, (9) MBAA-methoxybutyl adamantyl acrylate, (10) isobornyl acrylate, (11) isobornyl methacrylate, (12) cyclohexyl acrylate, and (13) cyclohexyl methacrylate The Other preferred acrylate monomers that can be used are: (14) 2-methyl-2-adamantyl methacrylate; (15) 2-ethyl-2-adamantyl methacrylate; (16) 3-hydroxy-1-adamantyl methacrylate; 3-hydroxy-1-adamantyl acrylate; (18) 2-methyl-2-adamantyl acrylate; (19) 2-ethyl-2-adamantyl acrylate; (20) 2-hydroxy-1,1,2-trimethylpropyl acrylate; (21) 5-oxo-4-oxatricyclo-non-2-yl acrylate; (22) 2-hydroxy-1,1,2-trimethylpropyl 2-methacrylate; (23) 2-methyl-2-adamantyl 2 -Methacrylate; (24) 2-ethyl-2-adamantyl 2-methacrylate; (25) 5-oxotetrahydrofuran-3-yl acrylate; (26) 3-hydride It is a non-2-yl 2-methyl acrylate - (28) 5-oxo-4-oxatricyclo; carboxy-1-adamantyl 2-methyl-acrylate; (27) 5-oxo-3-yl 2-methyl-acrylate.

  In one embodiment of the invention, a copolymer having polyhydroxystyrene (PHS) and one or more of the above acrylate monomers is part of the material that can be purified by the novel method of the invention. It should be understood that the polymerized other monomer species can be purified using the purification methods described herein. These monomer species include, but are not limited to, vinyl acetate, acrylic resins, styrene, styrene-acrylic resins, olefins such as ethylene and propylene, acrylonitrile, maleic anhydride, and mixtures thereof. The polymerization of these monomers can be carried out with cations, non-ions and / or free radicals. These are other embodiments of the present invention. However, the description provided herein is generally directed to styrene, styrene / acrylate, styrene / acrylate / norbornyl type monomers.

  The polymerization, purification and / or transesterification steps are performed on an anhydrous basis (ie, <about 5,000 ppm water). The alcohol solvent for the polymerization is an alcohol having 1 to 4 carbon atoms and is selected from the group consisting of methanol, ethanol, propanol, isopropanol, t-butanol and combinations thereof. The amount of solvent used is not critical and can be any amount that achieves the desired end result.

  The free radical initiator for the polymerization can be any initiator that achieves the desired end result. Initiators are 2,2'-azobis (2,4-dimethylpentanenitrile), 2,2'-azobis (2-methylpropanenitrile), 2,2'-azobis (2-methylbutanenitrile), 1, 1'-azobis (cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, diisononanoyl peroxide, decanoyl peroxide, oxalate peroxide, di (n- Propyl) peroxydicarbonate, di (sec-butyl) peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, t-butylperoxyneodecanoate, 2,5-dimethyl-2,5-di (2-ethyl) Hexanoylperoxy) hexane, t-amylperoxyneodecanoate, dimethyl 2,2'-azobisisobutyrate and combinations thereof It may be selected.

  Initiators are typically 2,2'-azobis (2,4-dimethylpentanenitrile), 2,2'-azobis (2-methylpropanenitrile), 2,2'-azobis (2-methylbutanenitrile) ), 1,1′-azobis (cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate and combinations thereof.

  The polymerization conditions are not critical and can be any temperature and pressure that produces the desired end result. Generally, the temperature is about 30 ° C to about 100 ° C, preferably about 40 ° C to about 100 ° C, and most preferably about 45 ° C to about 90 ° C. The pressure may be atmospheric pressure, reduced pressure, or overpressure. The polymerization time is not critical, but is generally done over at least 1 minute to produce a polymer of the corresponding composition.

After the polymerization step and before the transesterification step, the crude polymer is subjected to a purification procedure in which the crude polymer is purified by a multi-step separation process using the same type of alcohol solvent (first solvent). Additional first solvent is added to the crude polymer mixture and the resulting slurry is stirred vigorously and / or heated to boiling (about 66 ° C.) for several minutes, then cooled to about 25 ° C. and allowed to stand. By soaking, the slurry can be phase separated and the liquid is then removed by centrifugation, filtration, decantation or similar means. This method is repeated at least once more until no further purification is confirmed, for example, until a small sample of the decanted solvent evaporates to dryness and shows virtually no residue. This separation method, i.e. heating, cooling, separation and solvent substitution, is generally carried out 2 to 10 times.

One important measure of the purity of the crude polymer produced from the polymerization of the monomers is the polydispersity value. In general, for example, it is desirable to have a low value of less than about 3; a low value indicates that the polymerization reaction was more uniform in chain length. The uniqueness of this purification process is that the desired polymer produced is not soluble to some extent in the solvent, and undesirable low molecular weight average polymers and undesirable monomers are soluble in the solvent. Thus, a novel purification / separation step provides for the removal of these undesirable materials. In general, the polydispersity of the crude polymer is measured before, during and after this purification / separation step with the aim of reducing this value by at least about 10% of the value of the original crude polymer before the purification process. Preferably, it is desirable to provide a product with a polydispersity of about 2.0 or less. Polydispersity is gel permeation chromatography (GPC)
It should be understood to mean the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), as measured by

  In the transesterification step, the purified polymer from the polymerization step is subjected to the transesterification conditions in the presence of a catalytic amount of a base catalyst in an alcohol solvent. (It should be understood that after the purification step described above, some alcohol solvent still remains mixed with the desired polymer, but additional solvent should be added to keep the polymer in a fluid state. Transesterification could be carried out without the addition of this additional solvent, but the reaction would be more difficult and probably longer.) The base catalyst could be the alkyl acrylate monomer II, or the copolymerizable monomer ( EUCM) does not react substantially. The base catalyst is an alkali metal hydroxide or an alkali metal alkoxide. Base catalysts include lithium hydroxide, lithium methoxide, lithium ethoxide, lithium isopropoxide, sodium hydroxide, sodium methoxide, sodium ethoxide, sodium isopropoxide, potassium hydroxide, potassium methoxide, potassium ethoxide, It is selected from the group consisting of potassium isopropoxide, cesium hydroxide, cesium methoxide, cesium ethoxide, cesium isopropoxide and combinations thereof.

When the phenol blocking group is removed by hydrolysis, the acid is a strong acid member, for example, hydrochloric acid, hydrobromic acid, sulfuric acid.
Thus, according to the method of the present invention, after polymerization of the acyloxy-derived polymer and prior to transesterification, the crude polymer is subjected to this novel separation method, which separates the substantially purified polymer. The polymer can then be further processed.

  In another embodiment of the invention, solvent exchange is provided after the transesterification step (using a catalyst) and the catalyst removal step. In this solvent exchange step, the alcohol solvent (containing the purified polymer) is then replaced with an aprotic / organic solvent that is a photoresist compatible solvent, and the alcohol solvent is removed by distillation. The term “photoresist compatible solvent” refers to US Pat. No. 5,945,251 (column 4, lines 17-27), US 5,789,522 (column 13, lines 7-18) and US 5,939,511 (both about PGMEA). As described, PGMEA is widely used in photoresist technology as demonstrated in Examples 1 and 2 below). The contents of all these patents are incorporated herein by reference. The photoresist compatible solvent can be a member selected from the group of glycol ethers, glycol ether acetates, and aliphatic esters having no hydroxyl or keto groups. Examples of this solvent include glycol ether acetates such as ethylene glycol monoethyl ether acetate and propylene glycol monomethyl ether acetate (PGMEA).

The invention is further illustrated by the following examples which are given for illustrative purposes and are not intended to limit the scope of the invention in any way.
Example (outline)
In the examples below, the following abbreviations are used:
ASM: p-acetoxystyrene monomer
t-BPP: tert-butyl peroxypivalate
THF: tetrahydrofuran
GPC: Gel permeation chromatography
GC: Gas chromatography
FTIR: Fourier transform infrared spectroscopy
NMR: nuclear magnetic resonance spectroscopy, usually proton, ¹ H; and / or carbon 13, ¹³ C nucleus
DSC: Differential scanning calorimetry
UV-Vis: UV-Vis spectroscopy General analytical techniques used for characterization: Various analytical techniques were used to characterize the copolymers and terpolymers of the present invention:
NMR: ¹ H and ¹³ C NMR spectra were recorded on a Bruker 400 MHz spectrometer using a 5 mm probe at 400 and 100 MHz, respectively.

GPC: GPC was performed on a Waters gel permeation chromatograph equipped with refractive index detection.
GC: GC analysis was performed on a Hewlett Packard Model 5890 Series II gas chromatograph equipped with a DB-1 column.

FTIR: FTIR was recorded with Mattson Genesis Series FTIR.
DSC: Using the Perkin Elmer 7700 DSC, to measure the T _g of the copolymers and terpolymers of the present invention (glass transition temperature). The heating rate was generally maintained at 10 ° C / min over a temperature range of 50 ° C to 400 ° C. The nitrogen or air flow rate is maintained at 20 mL / min.

Samples were UV-Vised using a Hewlett Packard Vectra 486 / 33VL UV-Vis spectrometer.
Example 1
Poly (4-hydroxystyrene) in propylene glycol monomethyl ether acetate
To a four neck 12 liter flask equipped with a mechanical stirrer, condenser, nitrogen inlet and thermowell, 4-acetoxystyrene (2752.3 g, 16.97 mol) and methanol (3075.0 g) were added. The flask was purged with nitrogen and then heated to reflux (66 ° C.) for 1 hour. Then 2,2'-azobis (2,4-dimethylvaleronitrile) (146.0 g, 0.59 mol) was added to the hot reactor as a slurry in methanol (250 g). The reactor was heated to reflux for 2 hours, followed by an additional charge of 2,2′-azobis (2,4-dimethylvaleronitrile) (24.3 g, 0.1 mol). The reactor was heated for an additional 6 hours and then cooled to room temperature.

  The solids were extracted by continuous solvent replacement as described below. The reactor was heated to 60 ° C. with stirring. The heat was removed and the reactor was allowed to cool to 44.3 ° C. without stirring. The upper layer of solvent (899 g) was removed by suction and replaced with methanol (1495 g). The reactor was again heated to 60 ° C. and cooled to 41.9 ° C. without stirring. The upper layer (1700 g) was again removed by suction and replaced with methanol (1705 g). The reactor was again heated to 60 ° C. and cooled to 46.2 ° C. without stirring. The upper layer (1633 g) was again removed by suction and replaced with methanol (1765 g). The reactor was again heated to 60 ° C. and cooled to 45.0 ° C. without stirring. The upper layer (1905 g) was again removed by suction and replaced with methanol (1955 g). The reactor was again heated to 60 ° C. and cooled to 46.0 ° C. without stirring. The upper layer (2145 g) was again removed by suction and replaced with methanol (2215 g). The reactor was again heated to 60 ° C. and cooled to 46.0 ° C. without stirring. The upper layer (2241 g) was again removed by suction and replaced with methanol (1700 g). All solids between each extraction were analyzed for molecular weight by GPC (Table 1). The reactor was then cooled to room temperature.

  Purified poly (4-acetoxystyrene) was converted to poly (4-hydroxystyrene) as follows. The reactor was equipped with a Dean Stark trap and a condenser. A 25.0 wt% sodium methoxide solution in methanol (64.24 g, 0.30 mol) was added to the reactor. The reactor was then heated to reflux (64 ° C.). The overhead distillate was removed and replaced with an equal weight of methanol. The reactor was heated at reflux for 7.5 hours. The reactor was then cooled to room temperature. The solution was then passed through an Amberlyst A15 column (2 ″ × 16 ″) at room temperature at 40 ml / min to remove metal contamination.

  The solvent was changed from methanol to propylene glycol monomethyl ether acetate (PGMEA) as follows. The solution was added to a 4-neck 12 liter flask equipped with a distillation head and receiver, thermowell, mechanical stirrer and nitrogen inlet. The reactor was heated to 25 ° C. to 48 ° C. under vacuum (120 to 10 torr) to remove methanol. When the methanol was removed to the reactor, a total of 4975 g of PGMEA was added. The amount of solids present was measured by density and the solution was adjusted to 35.0% by weight with PGMEA. A total yield of 1634 g of polymer (81.7% theoretical yield) was obtained.

Example 2
Poly (4-hydroxystyrene) in propylene glycol monomethyl ether acetate
To a four neck 12 liter flask equipped with a mechanical stirrer, condenser, nitrogen inlet and thermowell, 4-acetoxystyrene (2752.3 g, 16.97 mol) and methanol (3081.0 g) were added. The flask was purged with nitrogen and then heated to reflux (66 ° C.) for 1 hour. Then 2,2′-azobis (2,4-dimethylvaleronitrile) (146.1 g, 0.59 mol) was added to the hot reactor as a slurry in methanol (250 g). The reactor was heated at reflux for 2 hours, followed by an additional charge of 2,2′-azobis (2,4-dimethylvaleronitrile) (24.4 g, 0.01 mol). The reactor was heated for an additional 6 hours and then cooled to room temperature.

  The solids were extracted by continuous solvent replacement as described below. The reactor was heated to 60 ° C. with stirring. The heat was removed and the reactor was allowed to cool to 45.0 ° C. without stirring. The upper layer of solvent (1129 g) was removed by suction and replaced with methanol (1817 g). The reactor was again heated to 60 ° C. and cooled to 47.0 ° C. without stirring. The upper layer (1627 g) was again removed by suction and replaced with methanol (1624 g). The reactor was again heated to 60 ° C. and cooled to 44.0 ° C. without stirring. The upper layer (1668 g) was again removed by suction and replaced with methanol (1613 g). The reactor was again heated to 60 ° C. and cooled to 47.0 ° C. without stirring. The upper layer (1514 g) was again removed by suction and replaced with methanol (1745 g). The reactor was again heated to 60 ° C. and cooled to 45.0 ° C. without stirring. The upper layer (1822g) was again removed by suction and replaced with methanol (2288g). The reactor was again heated to 60 ° C. and cooled to 43.0 ° C. without stirring. The upper layer (22471 g) was again removed by suction and replaced with methanol (1607 g). All solids between each extraction were analyzed for molecular weight by GPC (Table 1). The reactor was then cooled to room temperature.

  Purified poly (4-acetoxystyrene) was converted to poly (4-hydroxystyrene) as follows. The reactor was equipped with a Dean Stark trap and a condenser. A 25.0 wt% sodium methoxide solution in methanol (64.24 g, 0.30 mol) was added to the reactor. The reactor was then heated to reflux (64 ° C.). The upper distillate was removed and replaced with an equal weight of methanol. The reactor was heated at reflux for 7.5 hours. The reactor was then cooled to room temperature. The solution was then passed through an Amberlyst A15 column (2 ″ × 16 ″) at room temperature at 40 mL / min to remove metal contamination.

  The solvent was changed from methanol to propylene glycol monomethyl ether acetate (PGMEA) as follows. The solution was added to a 4-neck 12 liter flask equipped with a distillation head and receiver, thermowell, mechanical stirrer and nitrogen inlet. The reactor was heated to 25 ° C. to 48 ° C. under vacuum (120 to 10 torr) to remove methanol. When the methanol was removed to the reactor, a total of 4000 g of PGMEA was added. The amount of solids present was measured by density and the solution was adjusted to 35.0% by weight with PGMEA. A total yield of 1708 g of polymer (85.4% theoretical yield) was obtained.

Example 3
Poly (hydroxystyrene-co-ethoxyethoxystyrene)
To a 3 liter four neck round bottom flask containing 1.30 kg of PGMEA, 34.5 wt% polyhydroxystyrene solution, 400 mg of camphor sulfonic acid was added under nitrogen atmosphere and the mixture was placed at 23 ° C. for homogeneity. For 2 hours. The solution was then cooled to 5 ° C. and 127 g of ethyl vinyl ether was added dropwise with stirring at a reaction temperature of 5 ° C. to 10 ° C. (2 hours) under nitrogen. After the addition, the mixture was stirred at 5 ° C. for an additional 6 hours. 33 g Amberlyst A-21 pretreated with PGMEA was added to the reaction mixture and stirred at 25 ° C. for 2 hours. The resin was removed by filtration to give 1.43 kg, 39.3% poly (hydroxystyrene-co-ethoxyethoxystyrene) copolymer solution. Copolymer characterization and ratio measurements were performed by NMR. The hydroxystyrene / ethoxyethoxy-styrene ratio was determined to be 60/40, and the molecular weight was measured by GPC (polystyrene standard) with a polydispersity of 1.77 and Mw = 10,819.

Example 4
Poly (hydroxystyrene-co-t-butoxycarbonyloxystyrene)
To a 2 liter round bottom flask containing 1.03 kg, 35.1 wt% polyhydroxystyrene solution in PGMEA, 0.72 g of p-dimethylaminopyridine in 11 g of PGMEA was added under nitrogen and the mixture at 23 ° C. Stir for 1 hour. 124.4 g of di-t-butyl dicarbonate was added to the solution at 23 ° C. and stirred at 23 ° C. for 6 hours under nitrogen. A vacuum was applied to the solution at 20 mm Hg with stirring for 1 hour at 23 ° C. to remove carbon dioxide produced as a by-product in the solution. 30 g of Dowex Mac-3 pretreated with PGMEA was added to the reaction mixture and stirred at 23 ° C. for 2 hours. The resin was removed by filtration to give a 1.14 kg, 36.6 wt% poly (hydroxystyrene-co-t-butoxycarbonyloxystyrene) copolymer solution. Copolymer characterization and ratio measurements were performed by NMR. The hydroxystyrene / t-butoxycarbonyloxystyrene ratio was determined to be 82/18, and the molecular weight was determined by GPC to be Mw = 11,711 with a polydispersity of 1.67.

Example 5
The following examples illustrate the use of the process of the present invention in the purification of 4-acetoxystyrene / tert-butyl acrylate copolymers. 3282.8 g of 4-acetoxystyrene and 254 g of tert-butyl acrylate are polymerized in 3140 g of methanol using 204.3 g of tert-butyl peroxypivalate as a catalyst. A sample of the polymer is isolated for analytical purposes. After the polymerization was complete, 1390 g of methanol was removed at 58 ° C. and replaced with 1392 g of fresh methanol. The slurry was heated to reflux and cooled to 48 ° C. Another 1595 g of methanol was removed and replaced with 1590 g of fresh methanol. Again, the slurry was heated to reflux and cooled. The methanol was removed and replaced with 1800 g of fresh methanol, then the mixture was transesterified with 39.8 g of sodium methoxide. The polydispersity value of the purified polymer is 12% lower than that of the crude polymer.

  While specific reaction conditions, reactants and equipment have been described above to enable one skilled in the art to practice the invention, those skilled in the art will be able to make modifications and adjustments that are obvious extensions of the invention. Such obvious extensions or equivalents of the invention are intended to be within the scope of the invention as set forth in the claims.

Claims (7)

A method of transesterifying after purifying a crude polymer of polyacetoxystyrene homopolymer,
(A) suspending the crude polymer in an alcohol solvent and adding an additional alcohol solvent;
(B) heating and / or stirring for a time sufficient to allow dissolution of undesirable monomer impurities and oligomers in the crude polymer;
(C) cooling the resulting mixture;
(D) separating the alcohol solvent from the polymer;
(E) repeating the steps (a) to (d) until the polydispersity value of the purified polymer is 10% lower than the polydispersity value of the crude polymer;
(F) adding an additional alcohol solvent to the purified polymer obtained and transesterifying in the presence of a catalytic amount of a catalyst;
(G) passing the purified polymer, additional alcohol, and catalyst mixture through an ion exchange bed to remove the catalyst from the mixture; and (h) replacing the alcohol solvent with a photoresist compatible solvent. And wherein the steps (a) to (g) are performed on an anhydrous basis.   The method of claim 1, wherein the alcohol solvent is selected from the group consisting of methanol, ethanol, propanol, isopropanol, t-butanol, and mixtures thereof.   The method of claim 2, wherein the purified form of the polyacetoxystyrene homopolymer has a polydispersity value of less than 2.0.   The method of claim 2, wherein the alcohol solvent is methanol.   The method according to claim 1, wherein in the step (e), the steps (a) to (d) are repeated 2 to 10 times.   The method of claim 1, wherein the photoresist compatible solvent is selected from the group consisting of glycol ethers, glycol ether acetates, aliphatic esters having no hydroxyl or keto groups, and mixtures thereof. The method of claim 6 , wherein the photoresist compatible solvent is propylene glycol monomethyl ether acetate or ethyl lactate.